1. Field of the Invention
The present invention relates to an electric connector having a retention structure for preventing an insulated wire from coming off in the vertical direction at right angles to the wire axial direction.
2. Description of Related Art
A connector attached to an insulated wire has a resin housing and a contact (terminal metal fitting) secured to the housing. When there is used an insulation displacement contact having the arrangement that a slot for holding the core wire portion of an insulated wire is formed between a pair of insulation displacement blades for breaking up the insulation of the insulated wire, the contact and the core wire portion of the insulated wire can electrically be connected to each other merely by pushing the insulated wire into the slot of the insulation displacement contact. A connector using such an insulation displacement contact is called an insulation displacement connector.
In an insulation displacement connector, the retention force in the axial direction of an insulated wire (axial retention force) is obtained by nipping the core wire portion by the contact. However, the slot of the insulation displacement contact is opened in the vertical direction at right angles to the axial direction of the insulated wire. Therefore, when the wire is held only by the contact, the retention force in the vertical direction above-mentioned (orthogonal retention force) is insufficient. Accordingly, the housing has a retention structure for the insulation of the insulated wire.
More specifically, the housing is provided, in its position out of alignment with the contact in the axial direction of the insulated wire, with a wire holding groove for housing an insulated wire. Formed at the opening edges of the wire holding groove are wire hold-down pieces or strain relief pieces which project inwardly of the wire holding groove. At the same time when an insulated wire is mounted on an insulation displacement contact, the insulation of the wire is pushed to the wire hold-down pieces. As a result, the wire hold-down pieces are resiliently deformed and the wire holding groove is resiliently expanded and deformed. When the insulated wire gets over the wire hold-down pieces and is then housed in the wire holding groove, the wire hold-down pieces and the wire holding groove are restored in shape. Accordingly, when an external force is thereafter exerted, to the wire held in the wire holding groove, in the direction in which the wire is pulled out from the wire holding groove, the insulated wire is held within the wire holding groove under the action of the wire hold-down pieces. Thus, provision is made such that a sufficient orthogonal retention force is obtained (Japanese Patent Laid-Open Publication 2001-203008).
A connector to which a plurality of wires are connected, has contacts and wire holding grooves which respectively correspond to these wires. A plurality of wire holding grooves are formed in a row. However, when a plurality of wires are simultaneously mounted on the connector, the plurality of wire holding grooves are simultaneously expanded and opened. This causes the housing to be re-markably bent and deformed.
A connector used in a small-size device such as a digital still camera, a video camera, a cellular phone, a PDA (personal digital assistant) and the like, is extremely miniaturized in size, and is a multi-pole connector having a number of poles. When such a miniaturized and multi-pole connector is remarkably bent and deformed as above-mentioned, this involves the likelihood that the housing is broken in the step of mounting the insulated wires.
Further, in a miniaturized multi-pole connector, it can hardly be expected to resiliently deform the wire hold-down pieces due to their marginal miniaturization. Further, the insulations of insulated wires connected to the miniaturized multi-pole connector are very low in thickness. Thus, the deformation of the insulations can hardly be expected. Accordingly, the insertion of the insulated wires into the wire holding grooves has to rely solely on the resilient expansion and deformation of the wire holding grooves. Therefore, when the insulated wires are press-fitted, the housing is remarkably bent and deformed. This involves the likelihood that the housing is broken.
On the other hand, unless the housing is sufficiently bent and deformed, a plurality of insulated wires cannot be inserted into the wire holding grooves.
This dilemma can be solved by adopting the wire insertion method disclosed in Japanese Patent Laid-Open Publication 2002-260803. According to this prior art, the insulated wires are inserted in two steps including a first insertion step of pushing wires every other pole collectively into the housing by a punch, and a second insertion step of pushing wires every another pole collectively into the housing by another punch. It is there fore possible to insert the insulated wires into the housing without the housing remarkably bent and deformed at each insertion step.
According to this method, however, the wire insertion has to be divided into two steps, thus lowering the productivity. Further, a special punch has to be provided for holding down the wires every other pole.